Update all packages to the most recent version

To support this, the following changes have to be made as well:

- Ignore `package-lock.json` since NPM creates it, but we should not
  have it in the repository.
- Switch from `babel-preset-es2015` to `babel-preset-env` to resolve
  the deprecation warning in the test logs. The latter is more recent
  and flexible, but should be the same functionality-wise.
- `transform` now needs to have the `utf-8` encoding option provided.
  If not given, it will call the callback with a `Buffer` object,
  which results in an unhandled promise rejection since what is
  returned from the callback is a string, not a `Buffer`.

gulpfile.js

@@ -152,7 +152,7 @@ function createWebpackConfig(defines, output) {
           loader: 'babel-loader',
           exclude: /src\/core\/(glyphlist|unicode)/, // babel is too slow
           options: {
-            presets: pdfjsNext ? undefined : ['es2015'],
+            presets: pdfjsNext ? undefined : ['env'],
             plugins: ['transform-es2015-modules-commonjs'],
           },
         },
@@ -999,7 +999,7 @@ gulp.task('lib', ['buildnumber'], function () {
     content = preprocessor2.preprocessPDFJSCode(ctx, content);
     content = babel.transform(content, {
       sourceType: 'module',
-      presets: noPreset ? undefined : ['es2015'],
+      presets: noPreset ? undefined : ['env'],
       plugins: [
         'transform-es2015-modules-commonjs',
         babelPluginReplaceNonWebPackRequire,
@@ -1043,7 +1043,7 @@ gulp.task('lib', ['buildnumber'], function () {
       '!web/compatibility.js',
     ], { base: '.', }),
     gulp.src('test/unit/*.js', { base: '.', }),
-  ]).pipe(transform(preprocess))
+  ]).pipe(transform('utf8', preprocess))
     .pipe(gulp.dest('build/lib/'));
   return merge([
     buildLib,
@@ -1316,7 +1316,7 @@ gulp.task('dist-pre',
     license: DIST_LICENSE,
     dependencies: {
       'node-ensure': '^0.0.0', // shim for node for require.ensure
-      'worker-loader': '^0.8.0', // used in external/dist/webpack.json
+      'worker-loader': '^1.0.0', // used in external/dist/webpack.json
     },
     browser: {
       'fs': false,